U.S. patent application number 13/176214 was filed with the patent office on 2012-01-05 for synthesis of rare earth metal extractant.
This patent application is currently assigned to NISSIN CHEMICAL INDUSTRY CO., LTD.. Invention is credited to Masahiko Ikka, Tetsuya Kume, Hirochika Naganawa, Tetsuya Ohashi, Kazuaki Sakaki, Kojiro Shimojo, Hiroto Sugahara.
Application Number | 20120004458 13/176214 |
Document ID | / |
Family ID | 44514479 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120004458 |
Kind Code |
A1 |
Sakaki; Kazuaki ; et
al. |
January 5, 2012 |
SYNTHESIS OF RARE EARTH METAL EXTRACTANT
Abstract
A rare earth metal extractant in the form of a dialkyl diglycol
amic acid is synthesized by reacting diglycolic anhydride with a
dialkylamine in a synthesis medium. A molar ratio (B/A) of
dialkylamine (B) to diglycolic anhydride (A) is at least 1.0. A
non-polar or low-polar solvent in which the dialkyl diglycol amic
acid is dissolvable is used as the synthesis medium.
Inventors: |
Sakaki; Kazuaki;
(Echizen-shi, JP) ; Sugahara; Hiroto;
(Echizen-shi, JP) ; Ohashi; Tetsuya; (Echizen-shi,
JP) ; Kume; Tetsuya; (Echizen-shi, JP) ; Ikka;
Masahiko; (Echizen-shi, JP) ; Naganawa;
Hirochika; (Naka-gun, JP) ; Shimojo; Kojiro;
(Naka-gun, JP) |
Assignee: |
NISSIN CHEMICAL INDUSTRY CO.,
LTD.
Echizen-shi
JP
SHIN-ETSU CHEMICAL CO., LTD.
Tokyo
JP
|
Family ID: |
44514479 |
Appl. No.: |
13/176214 |
Filed: |
July 5, 2011 |
Current U.S.
Class: |
562/567 |
Current CPC
Class: |
C07C 231/02 20130101;
C07C 231/02 20130101; C07C 235/06 20130101 |
Class at
Publication: |
562/567 |
International
Class: |
C07C 231/02 20060101
C07C231/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 2010 |
JP |
2010-153161 |
Claims
1. A method for synthesizing a rare earth metal extractant in the
form of a dialkyl diglycol amic acid having the general formula
(1): ##STR00004## wherein R.sup.1 and R.sup.2 are each
independently alkyl, at least one being a straight or branched
alkyl group of at least 6 carbon atoms, comprising the step of
reacting diglycolic anhydride with a dialkylamine in a synthesis
medium, wherein dialkylamine (B) and diglycolic anhydride (A) are
present in a molar ratio (B/A) of at least 1.0, and the synthesis
medium is a non-polar or low-polar solvent in which the dialkyl
diglycol amic acid is dissolvable and which will serve as an
organic solvent to form an organic phase in subsequent solvent
extraction.
2. The method of claim 1 wherein the non-polar or low-polar solvent
is selected from the group consisting of toluene, xylene, hexane,
isododecane, kerosine, and higher alcohols.
3. The method of claim 1 wherein the molar ratio (B/A) of
dialkylamine (B) to diglycolic anhydride (A) is in a range of 1.0
to 1.2.
4. The method of claim 1 wherein the synthesis medium is used in
such an amount that the reaction solution at the end of reaction
may contain the dialkyl diglycol amic acid in a concentration of
0.1 mol/L to 1.5 mol/L.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No. 2010-153161 filed in
Japan on Jul. 5, 2010, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to a method for synthesizing an
extractant for extracting and separating a selected rare earth
element from a mixture of rare earth elements, specifically from a
mixture of at least two light rare earth elements (La, Ce, Pr, Nd,
Sm, and Eu) or from a mixture of at least one light rare earth
element and at least one other rare earth element inclusive of
yttrium.
BACKGROUND ART
[0003] In the modern society, rare earth elements are used in a
wide variety of applications, for example, as rare earth magnets,
phosphors, and electronic and electric materials in nickel hydrogen
batteries. With respect to the supply of rare earth elements, a
crisis of the rare earth resource is highlighted because the
producers are limited, the price lacks stability, and the demand is
expected to surpass the supply in the near future. For these
reasons, many attempts are made to reduce the amount of rare earth
element used and to develop a replacement. At the same time, it is
desired to establish a recycle system for recovering rare earth
elements as one valuable from in-process scraps produced during
manufacture of products and municipal wastes like electric and
electronic appliances collected from cities. Also there is an
urgent need for the research and development of new rare earth
mines.
[0004] Known methods for separating rare earth elements include
column extraction (or solid to liquid extraction) using ion
exchange resins, and solvent extraction (or liquid to liquid
extraction). Although the column extraction (or solid to liquid
extraction) method is simple in apparatus and easy in operation as
compared with the solvent extraction, it is small in extraction
capacity and discourages rapid treatment. The column extraction
method is thus used in the removal of a metal when the
concentration of a metal to be extracted in a solution is low, that
is, when the metal to be extracted is present as an impurity, as
well as in the waste water treatment. On the other hand, the
solvent extraction (or liquid to liquid extraction) method needs a
complex apparatus and cumbersome operation as compared with the
column extraction, but provides for a large extraction capacity and
rapid treatment. The solvent extraction method is thus used in
industrial separation and purification of metal elements. For the
separation and purification of rare earth elements that requires
efficient treatment of a large volume through continuous steps, the
solvent extraction method capable of such efficient treatment is
often used.
[0005] In the solvent extraction method, an aqueous phase
consisting of an aqueous solution containing metal elements to be
separated is contacted with an organic phase consisting of an
extractant for extracting a selected metal element and an organic
solvent for diluting the extractant. Then the metal element is
extracted with the extractant for separation.
[0006] Known extractants used in the art include tributyl phosphate
(TBP), carboxylic acids (e.g., Versatic Acid 10), phosphoric acid
esters, phosphonic acid compounds, and phosphinic acid compounds.
These extractants are commercially available. A typical phosphoric
acid ester is di-2-ethylhexylphosphoric acid (D2EHPA), a typical
phosphonic acid compound is 2-ethylhexylphosphonic
acid-mono-2-ethylhexyl ester (PC-88A by Daihachi Chemical Industry
Co., Ltd.), and a typical phosphinic acid compound is bis(2,4,4
trimethylpentyl)phosphinic acid (Cyanex 272 by Cytec
Industries).
[0007] The separation efficiency of the solvent extraction method
depends on a separation ability of the metal extractant,
specifically a separation factor. As the separation factor is
higher, the separation efficiency of the solvent extraction method
is higher, which enables simplification of separating steps and
scale-down of the separation apparatus, making the process
efficient and eventually leading to a cost reduction. A low
separation factor, on the other hand, makes the separation process
complex and poses a need for a large-scale separation
apparatus.
[0008] Even PC-88A which is known to have a high separation factor
for rare earth elements among the currently commercially available
extractants has a low separation factor between elements of close
atomic numbers, for example, a separation factor of less than 2,
specifically about 1.4 between neodymium and praseodymium which are
allegedly most difficult to separate among rare earth elements. The
separation factor of this value is not sufficient for separation
between neodymium and praseodymium. To separate them at an
acceptable purity, a large-scale apparatus must be installed at the
expense of cost. For more efficient separation of these elements,
there is a desire for the development of an extractant having a
higher separation factor than in the prior art and an
extracting/separating method using the same.
[0009] Dialkyl diglycol amic acids are known from JP-A 2007-327085
as the metal extractant having a high separation factor with
respect to rare earth elements, specifically light rare earth
elements such as lanthanum (La), cerium (Ce), praseodymium (Pr),
neodymium (Nd), and samarium (Sm). Using this extractant in solvent
extraction, the extraction/separation step of rare earth elements,
specifically light rare earth elements can be made more efficient.
In fact, better results are obtained from the extraction/separation
step of light rare earth elements using dialkyl diglycol amic acid
on a laboratory scale.
[0010] When dialkyl diglycol amic acid was used as the metal
extractant, satisfactory results were confirmed in a light rare
earth element extraction/separation experiment which was conducted
at a rare earth element concentration (C.sub.A: 0.01
mol/L.ltoreq.C.sub.A.ltoreq.0.7 mol/L) and a corresponding metal
extractant concentration (C.sub.0: 0.1
mol/L.ltoreq.C.sub.0.ltoreq.1.5 mol/L) which were practical
operating conditions of the rare earth element separating process
and in a light rare earth element extraction/separation experiment
using a countercurrent flow multi-stage mixer/settler of a
practically operating apparatus.
[0011] The dialkyl diglycol amic acid exhibits a satisfactory
separation factor in its performance as the metal extractant for
separating light rare earth elements, as mentioned above, and its
operating conditions have been surveyed. However, its synthesis has
not been fully established.
[0012] The known method for synthesizing the dialkyl diglycol amic
acid is in accord with the following reaction scheme.
##STR00001##
[0013] Herein R.sup.1 and R.sup.2 are each independently alkyl, and
at least one is a straight or branched alkyl group of at least 6
carbon atoms.
[0014] First, diglycolic anhydride is suspended in dichloromethane.
A secondary alkylamine in an amount slightly less than an equimolar
amount to the diglycolic anhydride is dissolved in dichloromethane
and the resulting solution is mixed with the suspension at 0 to
30.degree. C. As diglycolic anhydride reacts, the mixed solution
becomes clear. The reaction is completed when the solution becomes
clear. This is followed by removal of water-soluble impurities by
washing with deionized water, removal of water with a dehydrating
agent (e.g., sodium sulfate), filtration, and solvent removal.
Recrystallization from hexane is repeated plural times for
purification, yielding the desired product (see JP-A
2007-327085).
[0015] This synthesis method uses as the synthesis medium
dichloromethane which is one of the harmful substances listed in
several environmental pollution control laws, regulations and
Pollutant Release and Transfer Register (PRTR) in Japan and the
corresponding regulations in many countries. It is recommended to
avoid the substance.
[0016] The above synthesis method allegedly gives a yield of more
than 90% because it is conducted only on a laboratory scale where
the amount of synthesis is several grams.
[0017] However, a prominent drop of yield occurs when the synthesis
is enlarged to a scale of several kilograms or more. In fact, in a
synthesis experiment conducted on a scale of several hundreds of
grams, the yield decreases below 80%. Such a yield drop is
unwanted.
CITATION LIST
[0018] Patent Document 1: JP-A 2007-327085
SUMMARY OF INVENTION
[0019] An object of the invention is to provide a method for
synthesizing a rare earth metal extractant without a need for
dichloromethane which is used as reaction medium in the prior art
synthesis, the method being capable of improving the yield of the
reaction product and the efficiency of synthesis.
[0020] The inventors have found that in the synthesis of a dialkyl
diglycol amic acid serving as a rare earth metal extractant, better
results are obtained by reacting reactants, diglycolic anhydride
and a dialkylamine in a specific synthesis medium. Used as the
synthesis medium is a non-polar or low-polar solvent in which the
dialkyl diglycol amic acid is dissolvable and which will serve as
an organic solvent to form an organic phase in subsequent solvent
extraction. This method permits the dialkyl diglycol amic acid to
be effectively synthesized in high yields.
[0021] The invention provides a method for synthesizing a rare
earth metal extractant in the form of a dialkyl diglycol amic acid
having the general formula (1):
##STR00002##
wherein R.sup.1 and R.sup.2 are each independently alkyl, at least
one being a straight or branched alkyl group of at least 6 carbon
atoms, including the step of reacting diglycolic anhydride with a
dialkylamine in a synthesis medium. The dialkylamine (B) and
diglycolic anhydride (A) are present in a molar ratio (B/A) of at
least 1.0. Preferably the molar ratio (B/A) of dialkylamine (B) to
diglycolic anhydride (A) is in a range of 1.0 to 1.2. The synthesis
medium used herein is a non-polar or low-polar solvent in which the
dialkyl diglycol amic acid is dissolvable and which will serve as
an organic solvent to form an organic phase in subsequent solvent
extraction. The non-polar or low-polar solvent is typically
selected from among toluene, xylene, hexane, isododecane, kerosine,
and higher alcohols.
[0022] Also preferably the synthesis medium is used in such an
amount that the reaction solution at the end of reaction may
contain the dialkyl diglycol amic acid in a concentration C.sub.0
of 0.1 mol/L to 1.5 mol/L.
ADVANTAGEOUS EFFECTS OF INVENTION
[0023] According to the method of the invention, a dialkyl diglycol
amic acid which is an extractant having an improved separation
factor for light rare earth elements can be effectively synthesized
in high yields without a need for a harmful solvent,
dichloromethane. The method is of great worth in the industry.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a .sup.1H-NMR chart of the reaction product of
Example 1.
[0025] FIG. 2 is a .sup.1H-NMR chart of the reaction product of
Comparative Example 1.
DESCRIPTION OF EMBODIMENTS
[0026] The invention pertains to a rare earth metal extractant
which is a dialkyl diglycol amic acid having the general formula
(1).
##STR00003##
[0027] Herein R.sup.1 and R.sup.2 are each independently alkyl, at
least one of R.sup.1 and R.sup.2 being a straight or branched alkyl
group of at least 6 carbon atoms, preferably 6 to 18 carbon atoms,
and more preferably 7 to 12 carbon atoms. If the carbon count is
less than 6, the compound failing to play the role of extractant
because it is less lipophilic so that the organic phase lacks
stability and exhibits poor separation from the aqueous phase, and
because the dissolution of the extractant itself in aqueous phase
becomes noticeable. An excessive carbon count contributes to no
improvements in basic abilities like extraction and separation
abilities despite the increased cost of extractant manufacture. As
long as lipophilic nature is ensured, if one of R.sup.1 and R.sup.2
has a carbon count of at least 6, then the other may be of less
than 6 carbon atoms. For example, a compound of formula (1) wherein
two octyl (--C.sub.8H.sub.17) groups are introduced is most
preferred, which is named N,N-dioctyl-3-oxapentane-1,5-amic acid or
dioctyl diglycol amic acid (abbreviated as DODGAA,
hereinafter).
[0028] According to the invention, the dialkyl diglycol amic acid
is synthesized by reacting diglycolic anhydride with a dialkylamine
in a synthesis medium. The synthesis medium used herein is a
non-polar or low-polar solvent in which the dialkyl diglycol amic
acid is dissolvable and which will serve as an organic solvent to
form an organic phase in subsequent solvent extraction. For
example, diglycolic anhydride is suspended in an organic solvent
(which will form an organic phase in subsequent solvent
extraction), and the dialkylamine is dissolved in an organic
solvent (which will form an organic phase in subsequent solvent
extraction). The suspension and the solution are mixed together for
reaction to take place. The dialkylamine used herein is a secondary
alkylamine having alkyl groups corresponding to R.sup.1 and R.sup.2
in the dialkyl diglycol amic acid of formula (1).
[0029] The organic solvent which is used herein as the synthesis
medium and which will form an organic phase in subsequent solvent
extraction is a non-polar or low-polar solvent in which the dialkyl
diglycol amic acid is dissolvable. The non-polar or low-polar
solvent is a solvent having a dielectric constant of up to 15, for
example, having a low solubility in water, providing an appropriate
solubility for the extractant, having a low specific gravity, and
facilitating an extraction ability. Preferably the non-polar or
low-polar solvent is selected from among toluene, xylene, hexane,
isododecane, kerosine, and higher alcohols such as straight chain
alcohols of 5 to 8 carbon atoms. Use of such an organic solvent as
the synthesis medium eliminates a need for removal of the synthesis
medium and ensures that the organic solvent present in the reaction
solution may be used as the organic phase for solvent extraction
directly or, if necessary, after an additional amount of the
organic solvent is added so as to provide the organic phase with a
desired metal extractant concentration for solvent extraction.
[0030] If the synthesis medium is a solvent other than the
non-polar or low-polar solvent in which the dialkyl diglycol amic
acid is dissolvable and which will serve as an organic solvent to
form an organic phase in subsequent solvent extraction, then the
synthesis medium must be removed after the reactants are mixed and
reacted therein.
[0031] In the reaction step, an amount (B mol) of dialkylamine and
an amount (A mol) of diglycolic anhydride are used in a molar ratio
(B/A) of at least 1.0, preferably 1.0.ltoreq.B/A.ltoreq.1.2, and
more preferably 1.0.ltoreq.B/A.ltoreq.1.1. The resulting reaction
product contains unreacted dialkylamine as well as the desired
dialkyl diglycol amic acid. In the prior art method, plural times
of recrystallization are necessary to remove the unreacted
dialkylamine. It has been found that when solvent extraction is
carried out using dialkyl diglycol amic acid having dialkylamine
left therein, no problems arise with respect to separation
efficiency and phase separation, ensuring effective extraction and
separation. Specifically, even if the dialkylamine is left in the
metal extractant and the organic phase during solvent extraction,
it does not become an inhibitory factor to extraction and
separation and there is no need to remove it as an impurity. As a
result, the synthesis process can be simplified. A loss of the
reaction product by recrystallization is minimized. These
contribute to improved yields.
[0032] If B/A>1.2, the resulting reaction product may contain an
excess of unreacted dialkylamine as well as the desired dialkyl
diglycol amic acid. This reaction product may be used as the
extractant because no problems arise with respect to separation
efficiency and phase separation during solvent extraction. However,
use of excess dialkylamine is meaningless. Also the cost of
reactants for synthesis increases, rendering the method less cost
effective.
[0033] If B/A<1.0, which means an excess of diglycolic anhydride
for reaction, the desired dialkyl diglycol amic acid is obtained as
the reaction product, in which unreacted diglycolic acid may
remain. When solvent extraction is carried out using dialkyl
diglycol amic acid having diglycolic acid left therein, no
satisfactory separation ability is available and the solution
becomes white turbid because clad is formed between organic phase
and aqueous phase. This results in poor phase separation, failing
in normal extraction and separation. This is because the diglycolic
acid remaining along with the metal extractant, dialkyl diglycol
amic acid forms a complex with a rare earth metal ion, inhibiting
satisfactory extraction and separation. That is, diglycolic acid
becomes an inhibitory factor to extraction. To obtain diglycolic
acid-free dialkyl diglycol amic acid as the rare earth metal
extractant capable of normal extraction and separation, the step of
removing unreacted diglycolic acid is necessary as in the prior art
method. Specifically, the water-soluble diglycolic acid must be
removed by removing the synthesis solvent and washing the reaction
product with water. Upon water washing, however, the dialkyl
diglycol amic acid having a very low solubility in water
crystallizes and precipitates in the solvent (for example, a
solubility of DODGAA in water is 6.2.times.10.sup.-6 mol/L). In
order to use the dialkyl diglycol amic acid in crystallized form as
the rare earth metal extractant, filtration and drying steps are
needed. The process becomes less efficient because extra steps are
necessary as compared with the range of
1.0.ltoreq.B/A.ltoreq.1.2.
[0034] In a preferred embodiment of the method, the synthesis
medium is used in such an amount that the reaction solution at the
end of reaction may contain the dialkyl diglycol amic acid in a
concentration of 0.1 mol/L to 1.5 mol/L. Specifically, the amount
of dialkyl diglycol amic acid produced by the synthesis reaction is
previously computed from the amounts of reactants by the
stoichiometry in accord with the reaction scheme, and the amount of
the synthesis medium is adjusted such that the concentration
C.sub.0 of metal extractant or dialkyl diglycol amic acid in the
reaction solution may fall in a range: 0.1
mol/L.ltoreq.C.sub.0.ltoreq.1.5 mol/L, and more preferably 0.2
mol/L.ltoreq.C.sub.0.ltoreq.1.0 mol/L. The reaction solution
obtained in this preferred embodiment may be used as the organic
phase in subsequent solvent extraction directly, i.e., without a
need for concentration adjustment during subsequent solvent
extraction, for example, by adding a solvent such that the metal
extractant in the organic phase may be present in a predetermined
concentration applicable in the practical extraction step.
[0035] In case the extractant concentration C.sub.0<0.1 mol/L,
the dialkyl diglycol amic acid is produced by synthesis. However,
when this reaction product is used in solvent extraction on an
actual operation scale, the metal extractant concentration in the
organic phase is so low that only an aqueous solution having a
concentration of up to 0.03 mol/L of rare earth elements may be
treated. This entails a larger scale of separation apparatus and a
cost increase. It is very difficult, inefficient and impractical to
increase the extractant concentration from such a low level to a
high level for actual operation.
[0036] On the other hand, it is often difficult to set an
extractant concentration C.sub.0>1.5 mol/L, from considerations
of the solubility of the dialkyl diglycol amic acid in organic
solvents used in general solvent extraction methods. After the
synthesis reaction, a portion of the dialkyl diglycol amic acid
which is not dissolved in the solvent may crystallize and
precipitate out. Although the extra portion may be dissolved by
adding a solvent, surfactant or entrainer, the reaction product
solution is not efficient as the organic phase for solvent
extraction because the control of conditions for stable operation
becomes more complex.
EXAMPLE
[0037] Examples are given below by way of illustration and not by
way of limitation.
Example 1 and Comparative Example 1
Synthesis of Rare Earth Metal Extractant and Extraction/Separation
Test
[0038] DODGAA was synthesized by the method of the invention. The
DODGAA thus synthesized was examined for an ability to separate
rare earth metals from a mixture thereof by the solvent extraction
method.
[0039] First, 34.8 g (0.3 mol) of diglycolic anhydride was
suspended in 400 mL of hexane as synthesis medium. Separately, 72.4
g (0.3 mol) of dioctylamine was dissolved in 100 mL of hexane. With
stirring, the dioctylamine solution was added dropwise to the
diglycolic anhydride suspension.
[0040] Stirring was continued at room temperature until it was
confirmed that the solution became clear as a result of reaction of
diglycolic anhydride. The reaction product was obtained in hexane
solution (Example 1).
[0041] In Comparative Example 1, the same procedure as above was
repeated aside from using acetone as the reaction medium. The
reaction product was obtained in acetone solution.
[0042] Samples of the reaction products in Example 1 and
Comparative Example 1 were taken out and vacuum dried for solvent
removal, before they were analyzed by .sup.1H-NMR spectroscopy as
shown in FIGS. 1 and 2, respectively. The reaction products in
Example 1 and Comparative Example 1 were identified to be
DODGAA.
[0043] An extraction/separation test was performed. The
concentration of DODGAA in the reaction product solution of Example
1 or Comparative Example 1 was computed from the amounts of
reactants and synthesis medium. The reaction product solution was
diluted with hexane to form an organic solution having a DODGAA
concentration of 0.3 mol/L, which might become an organic
phase.
[0044] An aqueous solution containing mixed rare earth metals was
prepared by dissolving praseodymium chloride and neodymium chloride
in water in a molar ratio Pr:Nd of 1:1 and a concentration of 0.1
mol/L of Pr+Nd to form an aqueous solution, which might become an
aqueous phase. A separatory funnel was charged with 100 mL of the
organic solution and 100 mL of the aqueous solution and shaken at
20.degree. C. for about 20 minutes to effect extraction. After
equilibrium was reached, the liquid was allowed to separate into
organic and aqueous phases. A separatory funnel was charged with
100 mL of the thus separated organic phase and 100 mL of 5N
hydrochloric acid and shaken at 20.degree. C. for about 20 minutes
whereby the rare earth element once extracted into the organic
phase was back-extracted into the aqueous hydrochloric acid
solution. The concentrations of praseodymium and neodymium in the
aqueous phase and the back-extracted aqueous hydrochloric acid
solution were measured by an ICP atomic emission spectrometer
ICP-7500 (Shimadzu Corp.). The Nd/Pr separation factor and phase
separation are reported in Table 1.
TABLE-US-00001 TABLE 1 Synthesis Nd/Pr Phase medium separation
factor separation Example 1 hexane 2.5 definite Comparative acetone
2.5 indefinite Example 1
[0045] For the reaction product obtained in Example 1, its Nd/Pr
separation factor indicative of the separation ability as a metal
extractant was satisfactory, and the phase separation state was
definite. For the reaction product obtained in Comparative Example
1, its Nd/Pr separation factor was satisfactory, but it was
inadequate for solvent extraction as demonstrated by an indefinite
phase separation state. It is evident that when a dialkyl diglycol
amic acid is synthesized using as the synthesis medium a non-polar
or low-polar solvent in which the dialkyl diglycol amic acid is
dissolvable and which will serve as an organic solvent to form an
organic phase in subsequent solvent extraction, the process becomes
very efficient due to an eliminated need for solvent removal.
Examples 2 to 5 and Comparative Example 2
[0046] An amount (designated A in Table 2) of diglycolic anhydride
was suspended in 40 mL of hexane. Separately, an amount (designated
B in Table 2) of dioctylamine was dissolved in 10 mL of hexane.
With stirring, the dioctylamine solution was added dropwise to the
diglycolic anhydride suspension. Stirring was continued at room
temperature until it was confirmed that the solution became clear
as a result of reaction of diglycolic anhydride. The reaction
product was obtained in hexane solution. Table 2 also reports a
ratio B/A that is a ratio of the amount (B mmol) of dioctylamine to
the amount (A mmol) of diglycolic anhydride.
[0047] Samples of the reaction products were taken out and vacuum
dried for hexane removal, before they were analyzed by .sup.1H-NMR
spectroscopy, with DODGAA detected in all the products. A minor
amount of dioctylamine was detected in Examples 2, 3 and 5 while a
minor amount of diglycolic acid detected in Comparative Example
2.
[0048] An extraction/separation test was performed. The
concentration of DODGAA in the reaction product solution was
computed from the amounts of reactants and synthesis medium. The
reaction product solution was diluted with hexane to form an
organic solution having a DODGAA concentration of 0.3 mol/L, which
might become an organic phase.
[0049] An aqueous solution containing mixed rare earth metals was
prepared by dissolving praseodymium chloride and neodymium chloride
in water in a molar ratio Pr:Nd of 1:1 and a concentration of 0.1
mol/L of Pr+Nd to form an aqueous solution, which might become an
aqueous phase. A separatory funnel was charged with 100 mL of the
organic solution and 100 mL of the aqueous solution and shaken at
20.degree. C. for about 20 minutes to effect extraction. After
equilibrium was reached, the liquid was allowed to separate into
organic and aqueous phases. A separatory funnel was charged with
100 mL of the thus separated organic phase and 100 mL of 5N
hydrochloric acid and shaken at 20.degree. C. for about 20 minutes
whereby the rare earth element once extracted into the organic
phase was back-extracted into the aqueous hydrochloric acid
solution. The concentrations of praseodymium and neodymium in the
aqueous phase and the back-extracted aqueous hydrochloric acid
solution were measured by an ICP atomic emission spectrometer
ICP-7500 (Shimadzu Corp.). The extractant state, Nd/Pr separation
factor, and phase separation are reported in Table 2.
TABLE-US-00002 TABLE 2 A Ex- Nd/Pr diglycolic B tract- sepa- Phase
anhydride dioctylamine ant ration sepa- (g) (mmol) (g) (mmol) B/A
state factor ration Example 2 3.5 30.2 8.4 34.8 1.15 liquid 2.5
definite Example 3 3.5 30.2 8.0 33.1 1.10 liquid 2.5 definite
Example 4 3.5 30.2 7.3 30.2 1.00 liquid 2.5 definite Example 5 3.5
30.2 9.0 37.3 1.24 solid 2.5 definite Comparative 3.9 33.6 7.3 30.2
0.90 liquid -- indef- Example 2 inite
[0050] In Examples 2, 3 and 4 wherein a ratio of the amount (B
mmol) of dioctylamine to the amount (A mmol) of diglycolic
anhydride is 1.0.ltoreq.B/A.ltoreq.1.2, the Nd/Pr separation factor
indicative of the separation ability of a metal extractant and the
phase separation were satisfactory.
[0051] In Example 5 wherein B/A>1.2, the Nd/Pr separation factor
and the phase separation were satisfactory, but the reaction
product was difficult to handle as compared with the other products
because the excess dioctylamine in the reaction product solidified.
In Comparative Example 2, the excess diglycolic anhydride became an
inhibitory factor to extraction, causing indefinite phase
separation, and the Nd/Pr separation factor could not be
measured.
Examples 6 to 9
[0052] Diglycolic anhydride, 46.4 g (0.4 mol), was suspended in X
mL of hexane. Separately, 96.6 g (0.4 mol) of dioctylamine was
dissolved in Y mL of hexane. With stirring, the dioctylamine
solution was added dropwise to the diglycolic anhydride suspension.
Stirring was continued at room temperature until it was confirmed
that the solution became clear as a result of reaction of
diglycolic anhydride. The reaction product was obtained in hexane
solution. The amounts X and Y of hexane as the reaction medium are
shown in Table 3.
[0053] Samples of the reaction products were taken out and vacuum
dried for hexane removal, before they were analyzed by .sup.1H-NMR
spectroscopy, with DODGAA detected in all the products. The
concentration C.sub.0 of the reaction product (DODGAA) in the
hexane solution is shown in Table 3.
[0054] An extraction/separation test was performed using the hexane
solution of the reaction product (DODGAA) directly as an organic
solution which might become an organic phase.
[0055] An aqueous solution containing mixed rare earth metals was
prepared by dissolving praseodymium chloride and neodymium chloride
in water in a molar ratio Pr:Nd of 1:1 and a concentration (mol/L)
of Pr+Nd as shown in Table 4 to form an aqueous solution which
might become an aqueous phase. A separatory funnel was charged with
100 mL of the organic solution and 100 mL of the aqueous solution
and shaken at 20.degree. C. for about 20 minutes to effect
extraction. After equilibrium was reached, the liquid was allowed
to separate into organic and aqueous phases. A separatory funnel
was charged with 100 mL of the thus separated organic phase and 100
mL of 5N hydrochloric acid and shaken at 20.degree. C. for about 20
minutes whereby the rare earth element once extracted into the
organic phase was back-extracted into the aqueous hydrochloric acid
solution. The concentrations of praseodymium and neodymium in the
aqueous phase and the back-extracted aqueous hydrochloric acid
solution were measured by an ICP atomic emission spectrometer
ICP-7500 (Shimadzu Corp.). The Nd/Pr separation factor and phase
separation are reported in Table 4.
TABLE-US-00003 TABLE 3 DODGAA Amount X (mL) Amount Y (mL)
Concentration of hexane of hexane C.sub.0 (mol/L) Example 6 3200
800 0.1 Example 7 640 160 0.5 Example 8 320 80 1.0 Example 9 214 53
1.5
TABLE-US-00004 TABLE 4 Mixed rare earth metal Nd/Pr Phase
concentration (mol/L) separation factor separation Example 6 0.03
2.5 definite Example 7 0.10 2.5 definite Example 8 0.10 2.5
definite Example 9 0.50 2.5 definite
[0056] Examples 6 to 9 wherein the concentration C.sub.0 (mol/L) of
DODGAA was in the range: 0.1 mol/L.ltoreq.C.sub.0.ltoreq.1.5 mol/L
demonstrated a high separation factor and definite phase
separation.
[0057] Japanese Patent Application No. 2010-153161 is incorporated
herein by reference.
[0058] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *